The present invention relates to central air conditioning equipment having a common blower and branched ducts which lead to respective rooms from the common blower and, more particular, central air conditioning equipment having an air quantity control device in each branched duct.
In general, in central air conditioning equipment having no air quantity control device, cool air or warm air which is discharged at constant pressure and at constant air quantity by the blower is distributed to the respective rooms through the respective branched ducts, so that each room is cooled or warmed. Therefore, for example, when the quantity of air for a particular room is to be reduced by a damper in order to lower the temperature in the heating mode, the quantity of air which is distributed to other rooms increases so that the heating temperature in other rooms changes.
In order to solve this problem, air quantity control means which is disclosed in, for example, Japanese Patent Publication No. 55-24,022 and Japanese Patent Publication No. 55-22,696 has been conventionally developed.
In the former Japanese Patent Publication No. 55-24,022, changes of pressure in a common duct between an air conditioner and a terminal air quantity control device are detected, and the blower of the air conditioner is controlled to maintain the pressure at the detection section constant. However, with this control system, the following problem is still unsolved. Channel resistances differ between rooms which are close to the air conditioner and rooms which are away from the air conditioner even if the same quantity of air is exchanged. Therefore, the changes in pressure cause changes in the air quantity at the detection section. In order to obtain the predetermined air quantity, power which is required fo operating the blower cannot be maintained at minimum. In most cases, the blower is operated by excessive power. In this manner, blower operation results in energy loss and much noise in operation.
On the other hand, in Japanese Patent Publication No. 55-22,696, signals which instruct the proper air quantity for each terminal air quantity control device are added, and the addition output signal is supplied to a blower which is thus controlled in response to the above addition output signal. However, the above control system has drawbacks described below. When the total air quantity is changed because of the extension and reconstruction work of a building in which the air conditioning equipment has been installed, the control circuit must be rearranged and resynchronized with the blower. Further, when channel resistances vary from the air conditioner to each terminal air quantity control device, each terminal air quantity control device must be adjusted in accordance with the various channel resistances. This adjustment cannot properly be performed before the air conditioning equipment is installed, resulting in inconvenience.